Apparatus for coating



May 17, 1960 R. B. DUGGINS APPARATUS FOR COATING Filed March 14, 1958INVENTOR RAY BROWN DUGGINS QM 7Z% ATTORNEY This invention relates tocoating non-fibrous, organic sheet materials and more particularly, toan apparatus for coating films, webs and-sheets of regeneratedcellulose. Regenerated cellulose sheet material, as it comes from thecasting machine, possesses properties which limit its utilityessentially to ornamental and sanitary protective applications. However,the prior art is replete with coating compositions which serve tomake'the film commercially more attractive. There arecoatings to controlthe moisture andgas permeabilities of the film, to increase its chemicalresistance, to improve its heat-sealability, to add durability to thefilm and to improve surface slip and crease resistance of the film.

The coatings are usually applied from solutions or aqueous dispersionsby passing the regenerated cellulose film through a vessel, the diptank, containing the solution or dispersion. Thereafter, the coated filmis passed through a doctoring or smoothing device which regulates theamount of the coating composition left onthe film. The film is thendried, usually byheating to evaporate the volatile solvent or theaqueous dispersant. ,p I

More specifically, the film in the form of a continuous web' is led overa guide roll' into an ordinary tank in which a rod or roll or otherguide means is located. The guide roll is submerged in the liquid inthetank and thefilm web is led around it. The web emerges from the 'tank:ina substantially vertical'direction and; is then led to locations whereit is heated and dried. Prior to leaving the dipping location, the webis passed through the nip of doctor rolls to remove excess coatingliquid. These rolls may be located below, at, orabove the surthe face ofthe liquid in the tank. To prevent premature gelation of the coating, itis preferred to partially" submerge the doctor rolls-in the tank.

'The above-described'dlp-coatmg proeess has operated successfully formany years (refer to U.S. Patent No. 1,826,697, issued October 6, 1931).However, with the advent of high speed casting, i.e., 1'00 yards/minuteand above, with the accompanying necessity for coating at 7 high speeed,important problems have arisen. The appearance of coating smears on thesurface of the-film with the necessity for discarding such footagehas'made the increase in production almost futile. The smears are attheir worst when the doctor rolls, to prevent premature gelation of thecoating, are disposed at least partially below the surface of theliquid. The use of an aqueous dispersion rather than a solution as thecoating composition, while being economical in the use of water ratherthan an organic solvent, further intensifies the smear problem.

An object of the invention, therefore, is to provide an apparatus toreduce coating smears substantially. Other objects will appearhereinafter.

The objects are accomplished by an apparatus comprising a vessel adaptedto contain a coating composition liquid; guide means located in saidvessel below the level 2,936,733 Patented- May 17, 19 0 of the liquidtherein adapted to submerge the travelling web of film and to change itsdirection of travel from downwardly to substantially vertically upward;means located above the guide means and at least partially belowtheliquid level in said vessel adaptedto regulate the amount of coatingliquid on the surface of the emerging travelling'film; means disposedwithin'the pocket formed by the film web travelling downwardly and thensubstan tially upward adapted to feed coating liquid continuously intosaid vessel; and meansfor removing excess coating liquid from the vesseldisposed at the upper periphery of said vessel. Q

Figure 1 is a plan view ofrone embodiment of-the' apparatus of thepresent invention;

Figure 2 is a'sectional view along line 22 of Figure 1; and

Figure 3 is a plan view of another embodiment of the apparatus of thepresent invention.

Referring to the drawing, uncoated regenerated cellulose film- 10, theso-called base film, is unwound from roll 11 and is guided over roll 12into the dip tank'13 which contains a bath of the coating composition.Sub merged in the coating bath 14 of Figure 1 is a guide or dip rod 15,.around which" the film web is led in'th'e tank; The coated film asitemerges from the coating bath 14 passes through the nip of thejuxtaposed doctor rolls" 16 and 17 whereby excess'coating solution isremoved from the surface of the film. The doctor rolls are mounted onrotatable shafts 18 and 19, each of which extends at one end through thewalls of the tank to be rotated by means not shown, and which at theother end is journaled in a suitable hearing. The shafts are adjustablein the horizontal'plane for regulating the nip between thedoctor rollsand providing the desired coating thickness. The film 10, after passingbetween the doctor rolls,

is led into a dryer not shown wherein the solvent or the dispersant forthe coating composition is evaporated.

* The coating composition, either as a dispersion or in a solution, isled into the tank through a slotted distributor tube 20 criticallylocated in the envelope formed by the film and the doctor roll 16.Alternatively, as shown in Figure 3, the dip rod may be'hollow' andsuitably slotted to be a combination dip rod-distributor tube 21;However, the use of a distributor tube separate from the dip rod as inFigure 1 permits removal and cleaning of the distributor tube withoutdisturbing the" dip rod. It is also desirable that the slot 22 inFigure- 1 or 23in Figure 3 be located so that coating liquid feedsupwardly, substantially against roll 16. The coating liquid thus flowsupwardly andthe excess flows over the outer rim or p'eriphery of thevessel 13. ..--Additional inlets" for bath in the base or walls of thetank, although not necessary to the present invention, may be used atstart-up or to supply supplementary bath.

It is critical to the present invention that the coating compositionliquid be forced to overflow at a point or points on the rim of the diptank 13 remote from the place of emergence of the coated film from thetank. The means used to receive the overflow liquid is not important. InFigure 1 an appropriately sloped trough 24 surrounds the vessel 13.Overflow liquid is led through the trough and pipe 26 to the supplytank, not shown, located at a lower level wherein the coatingcomposition is replenished and pumped into the dip tank 13 through thedistributor rod as described previously. In Figure 3 a vessel 25 havingan opening in its base completely encases the vessel 13 to receiveoverflow liquid and to pass the liquid to the supply tank.

It is believed that the success of the present invention may beattributed to the critical locations of the entrance and exit of coatingcomposition liquid to and from 3 the dip tank, i.e the critical,location of the distributor tr be in the previously mentioned pocket orenvelope and the use ofthe overflow as a means of circulating thecoating composition liquid. At the high coating speeds required in thepresent competitive market, much foam. is created by air whipped intothe coating composition liquid by the rapidly moving film and by theagitation of the liquid by the rotating doctor rolls. It is believedthat this foam which accumulates on the surface. of the liquid in thedip tank passes into the nip of the doctor rolls and is squeezed intovarious areas on the surface of the film. It is these areas which maybecome visible after drying as coating smears. By the use ofthe presentinvention, any foam formed on the surface of the coating compositionliquid will be caused, to flow over the sides of the dip tank away fromthe travelling The apparatus is particularly advantageous for highspeed" coating regenerated cellulose film with aqueous dispersions ofvinylidene chloride polymers as described in, US. Patent No. 2,684,919,.In actual tests wherein regenerated cellulose film was coated withvinylidene chloride polymers, a 35% reduction in the amount of rejectedfor coating smears was noted when coating at speeds of 100-150yards/minute; a. 100% reduction was. noted at speeds above 150yards/minute over the prior art method wherein coating liquid wasbrought into the tank solely from-outside the aforementioned pocket andexcess liquid left through an outlet in the bottom of the tank.

Besides coating regenerated cellulose film, the invention; is applicableto coating other non-fibrous organic sheet materials such as polyesterfilms, cellulose ester films, polyamide films, polyethylene films, etc.with a variety of film-forming coatings from aqueous dispersions ororganic solvent solutions. More specifically, the aqueous dispersionsdescribed in US. Patent Nos. 2,278,415,; 2,570,478; and 2,684,919 andthe solvent solutions described in U.S Patent Nos. 1,826,696; 1,997,583;2,079,395; 2,205,210; 2,147,180; 2,236,546; 2,462,185; 2,686,744; and2,726,171 may be used to coat regenerated cellulose, cellulose acetate,ethyl cellulose, cellulose nitrate, vinylidene chloride polymers, nylon,polyethylene and polyethylene terephthalate films using the apparatus:13; the present invention. The sheet materials coated in the apparatusof the present invention are suitable for use as packaging materials forfood stufis, textiles, hard.- ware, etc., as tank linings, bottle capseals, etc.

Since many widely different embodiments of the apparatus can be designedwithout departing fromthe spirit and scope of this invention, it is,understood that the invention is not limited except as defined; by theappended claims.

What is claimed is:

15. Apparatus for coating a travelling-web ofzfilrn com,-

tion liquid; means disposed in said vessel below the level of liquidtherein adapted to guide a travelling web of film therearound; meansdisposed above said guide means adapted to regulate the amount'of'coating composition liquid on the surface of the emerging web offilm; means disposed solely within the pocket formed by the webtravelling around said guide means to feed coating composition liquidcontinuously; and means disposed at the periphery of said vessel forremoving excess coating compositionliquid from. said vessel.

2; An apparatus as in claim 1. wherein the guide means disposed in saidvessel is hollow, slotted and adapted also to serve as the means forfeedingcoating composition liquid continuously.

3. An apparatus as in claim 1 wherein said means adapted to regulate theamount of coating composition liquid on the surface of the emerging webof film is composed of two rotatable rolls spaced from each other injuxtaposition to provide a nip, theweb offilm passing through the niptherebetween.

4. An apparatus as in claim 3 wherein said rolls. are at least partiallysubmerged in the coating composition liquid in the vessel. I

5. Apparatus for continuously'coatingatravelling web of film comprisinga vessel adapted to contain a coating composition liquid; guide meansdisposed in said vessel below the level of'liquid therein adapted tosubmerge a travelling web of film and to change the direction of travelof said film from downward to substantially vertically upward; tworotatable rolls in juxtaposition to provide a nip therebetween disposedabove the guide means and at least partially below the level of liquidin the vessel-adapted to receive the emerging web of film therebetweenand to regulate the amount of coating composition liquid on the surfaceof the emerging web of film; an inlet for coating composition liquiddisposed solely within the envelope formed by the web of film travellingaround said guide means adapted to. feed coating compositionliquid'substantially upwardly and sub.- stantially toward one of saidrotatable rolls; and means disposed around the rim of said'vessel remotefrom the emerging web of film adaptedto receive overflowing coatingcoposition liquid.

6'. An apparatus as in claim 5 wherein said guide means is hollow,slotted and adapted to serve also asthe inlet for coating compositionliquid.

Koch Mar. 30, 19.26 2,357,536 .Sept., 5, 1944. 2,542,064 Feb. 20, 1951

